PROJECT SUMMARY/ABSTRACT Grating-based x-ray interferometric imaging has long been considered a promising technique to significantly enhance image quality at reduced radiation dose, by detecting phase and scattering contrasts in addition to the absorption. X-ray gratings are central components in x-ray interferometers. Commercially available x-ray gratings have periods of > 2 m, which limits the sensitivity enhancement to a level that the dose reduction enabled by interferometric imaging is not obvious for practical applications. Laboratory- made deep submicron period x-ray gratings have been used in prototype imaging systems to improve the imaging sensitivity by an order of magnitude. The small area of the gratings and the challenges to fabricate large area gratings limit the clinical applications of such imaging systems. The goal of this project is to develop a batch fabrication process to manufacture large area, submicron and deep submicron period x-ray phase gratings at energy levels up to 60 keV for various applications. The proposed research in Phase I will focus on fabrication of x-ray gratings for breast imaging applications at a central energy level of ~ 22 keV. Breast cancer is the top cancer in women worldwide. Early detection and treatment improve breast cancer outcome and survival, particularly before the cancer metastasizes. Digital mammography is the most popularly used imaging method for early detection of breast cancer. According to National Cancer Institute, the sensitivity is ~ 54% to 94% and the specificity is ~ 90%. X-ray interferometric imaging with submicron period gratings provides a promising solution to improve both the sensitivity and precision by combining the three contrast mechanisms, thus reducing both false negative and false positive rates. The lack of large area, submicron and deep submicron period gratings limit the further development of such imaging systems. General Optics proposes to bring such gratings to the market through developing a cost-efficient batch fabrication process. The specific aims of Phase I research are: (1) develop a process to fabricate 600 nm period, ?-phase shift x-ray gratings at 22 keV with an area of 6 cm x 6 cm; (2) develop a double- frequency process to produce 300 nm period, ?-phase shift x-ray gratings at 22 keV; (3) investigate the performance of these gratings via x-ray diffraction test. The investigation of the grating performance in x- ray interferometers, optimization of the grating profiles for better x-ray interferometer performance, further reduction of the grating period to 200 nm and the extension to 60 keV, ?-phase shift x-ray gratings would be the next stage of this SBIR Phase I project.